1. Field of the Invention
The present invention relates to a light-emitting apparatus housing a light-emitting element, and an illuminating apparatus employing the light-emitting apparatus.
2. Description of the Related Art
FIG. 4 is a sectional view showing a light-emitting apparatus of conventional design. In FIG. 4, the light-emitting apparatus is mainly composed of a base body 11, a reflection member 12, a light-emitting element 13 and a fluorescent material layer 14. The base body 11 is made of an insulator and has, at the center of its top surface, a placement portion 11a for emplacing thereon the light-emitting element 13. The base body 11 is also provided with a wiring conductor (not shown) formed of, for example, a metallized wiring line and a lead terminal for electrically conductively connecting within and without the light-emitting apparatus through the placement portion 11a and its environs. The reflection member 12 has a frame-like form and is fixedly bonded to the top surface of the base body 11. An inner surface 12a of the reflection member 12 is inclined so as to extend outward gradually in an upward direction and is shaped into a reflection surface for reflecting light emitted from the light-emitting element 13. The fluorescent material layer 14 is composed of a light transmitting member that contains a fluorescent material (not shown) for performing wavelength conversion on the light emitted from the light-emitting element 13.
The base body 11 is made of a ceramic material such as sintered aluminum oxide (alumina ceramics), sintered aluminum nitride, sintered mullite, or glass ceramics, or a resin material such as epoxy resin. In a case where the base body 11 is made of a ceramic material, on the top surface thereof is formed a wiring conductor by firing a metal paste of tungsten (W) or molybdenum (Mo)-manganese (Mn) at a high temperature. On the other hand, in a case where the base body 11 is made of a resin material, a molded lead terminal made of copper (Cu) or an iron (Fe)-nickel (Ni) alloy is fixedly arranged within the base body 11.
The reflection member 12 is formed of a metal material such as aluminum (Al) or an Fe—Ni-cobalt (Co) alloy, or a ceramic material such as alumina ceramics, or a resin material such as epoxy resin, through a a cutting process, or a molding technique such as die-molding or extrusion.
Moreover, the reflection member 12 has its inner surface 12a shaped into a reflection surface for reflecting light emitted from the light-emitting element 13 or the fluorescent material layer 14. The inner surface 12a is finished off by coating thereon a metal such as Al by means of vapor deposition or plating. The reflection member 12 is finally joined to the top surface of the base body 11, with use of a bonding material such as solder, a brazing filler material such as silver (Ag) brazing filler, or a resin adhesive, in such a way that the placement portion 11a is surrounded by the inner surface 12a. 
The light-emitting element 13 is constituted by forming a light-emitting layer on a monocrystalline substrate such as a sapphire substrate by means of the liquid-phase growth method or MOCVD method. The examples of materials used for the light-emitting layer include: a gallium (Ga)—Al-nitride (N) compound; a zinc (Zn)-sulfur (S) compound; a Zn-selenium (Se) compound; a silicon (Si)-carbon (C) compound; a Ga-phosphorus (P) compound; a Ga—Al-arsenic (As) compound; an Al-indium (In)—Ga—P compound; an In—Ga—N compound; a Ga—N compound; and an Al—In—Ga—N compound. The light-emitting element 13 may have a homo structure, a hetero structure, or a double-hetero structure including an MIS junction or PN junction. The luminescence wavelength of the light-emitting element 13 shall be selected according to the material used for the light-emitting layer and its mix crystal ratio, for example, in a range from ultraviolet to infrared regions. The light-emitting element 13 is, at its electrode, electrically connected to the wiring conductor arranged near the placement portion 11a by using a bonding wire (not shown) or by adopting a flip-chip bonding method. In regard to the flip-chip bonding method, the light-emitting element 13 is arranged with the electrode side down, and connection is established through a solder bump.
The fluorescent material layer 14 is formed in the shape of a plate by subjecting a light transmitting member such as epoxy resin or silicone resin charged with a fluorescent material to a heat-hardening process. By arranging the fluorescent material layer 14 so as to cover the opening of the reflection member 12, visible or ultraviolet light with the luminescence wavelength emitted from the light-emitting element 13 can be absorbed and converted into light with longer wavelength. Thus, various materials may be used for the fluorescent material layer 14 in consideration of the luminescence wavelength of the light emitted from the light-emitting element 13, as well as desired light emitted from the light-emitting apparatus, whereby making is possible to realize a light-emitting apparatus with which light having a desired wavelength spectrum can be taken out. Moreover, the light-emitting apparatus is allowed to emit white light under conditions where the light emitted from the light-emitting element 13 and the light emitted from the fluorescent material are in a complementary-color relation to each other.
The preferred examples of the fluorescent material in use include: a cerium (Ce)-activated yttrium aluminum garnet-based fluorescent material; a perylene derivative; copper (Cu)—Al-activated zinc cadmium sulfide; manganese (Mn)-activated magnesium oxide; and titanium oxide. The fluorescent material may be formed of either a single substance or a mixture of two or more different substances.
Related art is disclosed in Japanese Unexamined Patent Publication JP-A 2000-349346.
However, the above-described conventional light-emitting apparatus has a simple structure in which the inner surface 12a is inclined rectilinearly so as to extend outward gradually in an upward direction. Inconveniently, in this structure, part of the light emitted from the light-emitting element 13 is reflected from the inner surface 12a over and over again until it is shone onto the fluorescent material layer 14. As a result, the intensity of the light emitted from the light-emitting element 13 is reduced due to light absorption caused by the reflection member 12. This gives rise to a problem of the radiation light intensity and brightness in the light-emitting apparatus being significantly deteriorated.
Furthermore, part of the light emitted from the light-emitting element 13 and reflected from the inner surface 12a enters the fluorescent material layer 14 at an incident angle larger than the critical reflection angle. This causes total reflection of light in a lower surface of the fluorescent material layer 14, and thus wavelength conversion is no longer effected by the fluorescent material. As a result, there arises a problem of the radiation light intensity and brightness in the light-emitting apparatus being significantly deteriorated.
In addition, some light emitted from the light-emitting element 13 in an upward direction enters the fluorescent material layer 14 without being incident upon the inner surface 12a. Part of this light undergoes total reflection on the lower surface of the fluorescent material layer 14 at an angle larger than the critical angle. As a result, the efficiency of wavelength conversion effected by the fluorescent material is decreased, which leads to a problem of the radiation light intensity and brightness in the light-emitting apparatus being significantly deteriorated.